72 Stiufics on Soil Protozoa 



case. After the bacterial counts were made the soil samples were 

 covered with soil extract --. K,HP04 and incubated for seven days at 

 22° C. At the end of this period the cultures so made from Nos. 3, 4, 7 

 and 8 contained active protozoa. Nos. 7 and S showed decidedly 

 larger numbers than did 3 and 4. The remaining four soil samples as 

 well as the controls showed no protozoa. But the original "sterilised" 

 soil and the controls contained numerous bacteria. 



Table 19. 



From the results here given it is probable that the inoculated 

 protozoa have been active in Nos. 7 and 8. But the period of activity 

 under the conditions of the experiment must have been a short one, as 

 after the single watering the soil would very soon become too dry for 

 active life. This, in all probability, accounts for the comparatively 

 small depression in bacterial numbers. 



For the confirmatory experiment the soil was sterilised with formalin 

 in the flasks in which it was to be subsequently used. Quantities of 

 50 grams of air-dry sieved soil were rubbed up in a mortar with 2 c.c. 

 of a solution containing 5 c.c. formalin + 3.5 c.c. water. Forty-five 

 grams of the soil was immediately weighed out into each of the flasks. 

 The flasks used were small Erlenmeyers closed by tight-fitting corks. 

 The formalin was allowed to act for six days and was then decomposed 

 with slaked lime as described in the last experiment. Each flask 

 received 5 c.c. of a sterile suspension of .5 grams Ca(OH),, in 100 c.c. 

 water (water content of soil in flasks = 70 % w.h.c). The flasks 

 were placed in the 38° C. incubator for 24 hours. The soil in each 

 was thoroughly broken up with a sterile spatula and the flasks put 

 back in the incubator for another day. The corks were then replaced 

 by sterile cotton-wool stoppers and the flasks weighed. After several 



